Particle Deposition Characteristics and Efficiency in Duct Air Flow over a Backward-Facing Step: Analysis of Influencing Factors

Dry deposition of airborne particles in duct air flow over a backward-facing step (BFS) is commonly encountered in built environments and energy engineering. However, the understanding of particle deposition characteristics in BFS flow remains insufficient. Thus, this study investigated particle deposition behaviors and efficiency in BFS flow by using the Reynolds stress model and the discrete particle model. The influences of flow velocities, particle diameters, and duct expansion ratios on particle deposition characteristics were examined and analyzed. After numerical validation, particle deposition velocities, deposition efficiency, and deposition mechanisms in BFS duct flow were investigated in detail. The results showed that deposition velocity in BFS duct flow monotonically increases when particle diameter increases. Moreover, deposition velocity falls with increasing expansion ratio but rises with increasing air velocity. Deposition efficiency, the ratio of deposition velocity, and flow drag in a BFS duct is higher for small particles but lower for large particles as compared with a uniform duct. A higher particle deposition efficiency can be achieved by BFS with a smaller expansion ratio. The peak deposition efficiency can reach 33.6 times higher for 1-μm particles when the BFS expansion ratio is 4:3. Moreover, the “particle free zone” occurs for 50-μm particles in the BFS duct and is enlarged when the duct expansion ratio increases.

Download Full-text

Investigation of particle deposition efficiency enhancement in turbulent duct air flow by surface ribs with hybrid-size ribs

Indoor and Built Environment ◽

10.1177/1420326x16662509 ◽

2016 ◽

Vol 26 (5) ◽

pp. 608-620 ◽

Cited By ~ 2

Author(s):

Hao Lu ◽

Lin Lu

Keyword(s):

Particle Deposition ◽

Air Flow ◽

Deposition Efficiency ◽

Dynamics Simulation ◽

Particle Model ◽

Particle Removal ◽

Cleaning Equipment ◽

Discrete Particle Model ◽

Turbulent Air Flow ◽

Flow Drag

This study presents the particle deposition enhancement by hybrid-size and same-size surface ribs in turbulent air duct flows using computational fluid dynamics simulation. The Reynolds stress turbulence model with UDF corrections and discrete particle model were adopted to simulate the turbulent air flow fields and particle deposition behaviours, respectively. After numerical validation with the relative literature results, pure particle deposition enhancement ratios, flow drag increase, comprehensive deposition efficiency and deposition enhancement mechanisms were investigated and discussed in details. The findings showed that the hybrid-size ribs with small rib spacing have the best enhancement performance on particle deposition for small particles ([Formula: see text]). Considering the flow drag increase, the maximum deposition efficiency can reach 485 for 1 µm particles for the hybrid-size ribbed cases, while it is just 425 for the same-size ribbed case. Nevertheless, no obvious particle deposition enhancement can be found for large particles ([Formula: see text]) for all types of surface ribs. The hybrid-size surface ribs are more efficient compared with the same-size ribs, which can be applied in the air cleaning equipment to improve the aerosol particle removal performance.

Download Full-text

Numerical Simulation of the Aerosol Particle Motion in Granular Filters with Solid and Porous Granules

Processes ◽

10.3390/pr9020268 ◽

2021 ◽

Vol 9 (2) ◽

pp. 268

Author(s):

Olga V. Soloveva ◽

Sergei A. Solovev ◽

Ruzil R. Yafizov

Keyword(s):

Numerical Simulation ◽

Aerosol Particle ◽

Particle Deposition ◽

Particle Diameter ◽

Deposition Efficiency ◽

Hydrodynamic Resistance ◽

Hydrodynamic Properties ◽

Granular Filters ◽

Limiting Value ◽

Good Agreement

In this work, a study was carried out to compare the filtering and hydrodynamic properties of granular filters with solid spherical granules and spherical granules with modifications in the form of micropores. We used the discrete element method (DEM) to construct the geometry of the filters. Models of granular filters with spherical granules with diameters of 3, 4, and 5 mm, and with porosity values of 0.439, 0.466, and 0.477, respectively, were created. The results of the numerical simulation are in good agreement with the experimental data of other authors. We created models of granular filters containing micropores with different porosity values (0.158–0.366) in order to study the micropores’ effect on the aerosol motion. The study showed that micropores contribute to a decrease in hydrodynamic resistance and an increase in particle deposition efficiency. There is also a maximum limiting value of the granule microporosity for a given aerosol particle diameter when a further increase in microporosity leads to a decrease in the deposition efficiency.

Download Full-text

The Influence of Volume Surface Ratio of Rectangle Air-Conditioning Duct on Particle Deposition

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.71-78.3633 ◽

2011 ◽

Vol 71-78 ◽

pp. 3633-3638 ◽

Cited By ~ 1

Author(s):

Jie Zhang ◽

Ze Hua Liu ◽

Yuan Quan Liu ◽

Hui Min Li ◽

Yong Fei Ning

Keyword(s):

Cross Section ◽

Air Conditioning ◽

Particle Deposition ◽

Deposition Velocity ◽

Vertical Wall ◽

Influence Factors ◽

Particle Model ◽

Random Trajectory ◽

Air Speed ◽

The Given

This paper discusses particle deposition in rectangle air-conditioning duct using RSM (Reynold Stress Model) and random trajectory particle model. Particle with nominal diameters of 10-200μm are simulated at each of three nominal air speed: 4m/s, 6m/s and 8m/s, respectively, in the cross-section sizes of 160×120, 500×250, 1000×320mm. In simulation, the paper compares and analyzes the influence factors of particles deposition in volume surface ratio of the given duct. The results show that: 1) particle deposition velocity increases with volume surface ratio; 2) As the inlet air speed increasing, when the particles deposited to floor and vertical wall, the image of dimensionless deposition velocity Vs dimensionless relaxation time shows a coincident trend when the duct cross-section sizes are 500×250, 1000×320mm, but has great differences with the image of 160×120mm.

Download Full-text

PIV Measurements in Square Backward-Facing Step

Journal of Fluids Engineering ◽

10.1115/1.2746896 ◽

2007 ◽

Vol 129 (8) ◽

pp. 984-990 ◽

Cited By ~ 8

Author(s):

Mika Piirto ◽

Aku Karvinen ◽

Hannu Ahlstedt ◽

Pentti Saarenrinne ◽

Reijo Karvinen

Keyword(s):

Shear Stress ◽

Reynolds Stress ◽

Reynolds Shear Stress ◽

Experimental Tests ◽

Expansion Ratio ◽

Spanwise Direction ◽

Duct Flow ◽

Backward Facing Step ◽

Mean Velocity ◽

Stress Profiles

Measurements with both two-dimensional (2D) two-component and three-component stereo particle image velocimetry (PIV) and computation in 2D and three-dimensional (3D) using Reynolds stress turbulence model with commercial code are carried out in a square duct backward-facing step (BFS) in a turbulent water flow at three Reynolds numbers of about 12,000, 21,000, and 55,000 based on the step height h and the inlet streamwise maximum mean velocity U0. The reattachment locations measured at a distance of Δy=0.0322h from the wall are 5.3h, 5.6h, and 5.7h, respectively. The inlet flow condition is fully developed duct flow before the step change with the expansion ratio of 1.2. PIV results show that the mean velocity, root mean square (rms) velocity profiles, and Reynolds shear stress profiles in all the experimental flow cases are almost identical in the separated shear-layer region when they are nondimensionalized by U0. The sidewall effect of the square BFS flow is analyzed by comparing the experimental statistics with direct numerical simulation (DNS) and Reynolds stress model (RSM) data. For this purpose, the simulation is carried out for both 2D BFS and for square BFS having the same geometry in the 3D case as the experimental case at the lowest Reynolds number. A clear difference is observed in rms and Reynolds shear stress profiles between square BFS experimental results and DNS results in 2D channel in the spanwise direction. The spanwise rms velocity difference is about 30%, with experimental tests showing higher values than DNS, while in contrast, turbulence intensities in streamwise and vertical directions show slightly lower values than DNS. However, with the modeling, the turbulence statistical differences between 2D and 3D RSM cases are very modest. The square BFS indicates 0.5h–1.5h smaller reattachment distances than the reattachment lengths of 2D flow cases.

Download Full-text

Turbulent Two-Phase Flows and Particle Deposition in a Duct at High Concentrations

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 2, Fora ◽

10.1115/fedsm-icnmm2010-30828 ◽

2010 ◽

Author(s):

Goodarz Ahmadi ◽

Hojjat Nasr ◽

John B. McLaughlin

Keyword(s):

Particle Deposition ◽

Deposition Velocity ◽

Particle Collision ◽

Duct Flow ◽

Particle Collisions ◽

Coupling Effects ◽

Two Phase Flows ◽

Two Phase ◽

Mean Velocity ◽

Navier Stokes Equation

Two-phase flows including particle-particle collisions and two-way coupling in a turbulent duct flow were simulated using a direct simulation approach. The direct numerical simulation (DNS) of the Navier-Stokes equation was performed via a pseudospectral method was extended to cover two-way coupling effects. The effect of particles on the flow was included in the analysis via a feedback force that acted on the fluid on the computational grid points. The point particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. Several simulations for different particle relaxation times and particle mass loading were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration were determined. It was found that when particle-particle collisions were included in the computation, the particle deposition velocity increased. When the particle collision was neglected but the particle-fluid two-way coupling was accounted for, the particle deposition velocity decreased slightly. When both inter-particle collisions and two-way coupling effects were taken into account in the simulations, the particle deposition velocity increased. Comparisons of the present simulation results with the available experimental data and earlier numerical results are also presented.

Download Full-text

Comparison of Micro- and Nano-Size Particle Transport and Depositions in 90 Degree Bend Microchannel

ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 3 ◽

10.1115/mnhmt2009-18045 ◽

2009 ◽

Author(s):

Kai Zhang ◽

Jianzhong Lin ◽

Mingzhou Yu

Keyword(s):

Particle Size ◽

Electric Field ◽

Finite Volume Method ◽

Finite Volume ◽

Particle Deposition ◽

Particle Diameter ◽

Deposition Efficiency ◽

Size Particle ◽

Volume Method ◽

Nano Size

The flow and electric field are simulated numerically with finite volume method first, then large number of nanoparticles and microparticles are injected into the microchannel separately, and these particles are traced with the Lagrangian method. It has been found that particle deposition efficiency in the bend usually decreases first then increases with particle size increasing, and there usually exists a minimum value and it corresponds to the particle diameter of about 3μm, which means that kind of particle can transport longer distance. The electric field doesn’t affect that specified value. This conclusion is helpful to the optimization of the design of microchips.

Download Full-text

Numerical Simulation of Particles Deposition in a Human Upper Airway

Advances in Mechanical Engineering ◽

10.1155/2014/207938 ◽

2014 ◽

Vol 6 ◽

pp. 207938 ◽

Cited By ~ 1

Author(s):

Debo Li ◽

Qisheng Xu ◽

Yaming Liu ◽

Yin Libao ◽

Jin Jun

Keyword(s):

Numerical Simulation ◽

Nasal Cavity ◽

Particle Deposition ◽

Geometric Model ◽

Particle Diameter ◽

Upper Airway ◽

Deposition Efficiency ◽

Particle Movement ◽

Scanned Images ◽

Les Model

Based on the CT scanned images, a realistic geometric model from nasal cavity to upper six-generation bronchia is rebuilt. In order to effectively simulate the particle movement and deposition, LES model is used and the particles are tracked in the frame of Lagrange. Seven kinds of typical particles, including micron particles (1, 5, and 10 μm) and nanoparticles (1, 5, 20, and 100 nm), and three representative respiratory intensities are adopted as computational case, respectively. Deposition efficiency ( D E), deposition concentration ( D C), and capture efficiency ( C E) are introduced. Furthermore, the locations of particle deposition are visualized. The results indicate that the injecting particles from different nasal inlet present “transposition effect.”The D E values of micron particles are much higher than nanoparticles. The particle diameter plays a weaker role in nanoparticle depositions than micron particles. The highest values of D E and D C both occur in nasal cavity, while the highest C E up to 99.5% occurs in bronchus region.

Download Full-text

Deposition of naphthalene particle in horizontal straight pipe of manufactured gas pipeline

Advances in Mechanical Engineering ◽

10.1177/1687814018793568 ◽

2018 ◽

Vol 10 (8) ◽

pp. 168781401879356

Author(s):

Qian Li ◽

Xiaonan Wu ◽

Siying Yu ◽

Lianqing Li ◽

Xinxin Wang

Keyword(s):

Particle Size ◽

Deposition Rate ◽

Particle Deposition ◽

Deposition Velocity ◽

Particle Diameter ◽

Gas Pipeline ◽

Discrete Phase Model ◽

Straight Pipe ◽

Inlet Velocity ◽

Time Operation

After long time operation of the manufactured gas pipeline, the naphthalene in the gas will jam the pipeline and threaten the safety of the pipeline seriously. To study the naphthalene particle deposition law in the manufactured gas pipeline, a horizontal straight pipe of Kunming manufactured gas pipeline is taken as an example; based on Reynolds stress model and discrete phase model, ANSYS Fluent software is used to carry out the numerical simulation in different pipe diameters, particle size, inlet velocity, temperature, and pressure conditions. The main conclusion can be obtained as follows (1) in the horizontal straight pipe section, particle diameter and temperature are positively correlated with the deposition rate and the deposition velocity of naphthalene particle and the inlet velocity and pressure are negatively correlated with them; (2) the naphthalene particle deposition rate is mainly affected by the particle size and the inlet velocity; (3) the larger the pipeline diameters, the greater the particle mass flow rate under the same particle inlet concentration, the lower the carrying capacity of the fluid to particles, the greater the naphthalene particle deposition rate; (4) the naphthalene particle deposition can be suppressed by increasing the gas transmission velocity and pressure and reducing the temperature, thus ensuring the safe operation of manufactured gas pipeline.

Download Full-text